A blast was heard on Thursday from vacant land behind the magistrate’s court in the town of Pugoda, 40 km (25 miles) east of the capital Colombo, police and local residents said. Sri Lanka central bank workers are also on lockdown, having been told to remain in Colombo HQ building and security have been warned there could be an explosion nearby, according to two bank sources. Also, the entry road to Colombo’s main airport was closed after a suspicious vehicle was seen at a nearby car park, according to airport police.

It was later found to be a false alarm, according to an air force spokesman.

The street outside the bank, which is near the World Trade Centre, is blocked to traffic.

Police spokesman Ruwan Gunasekera said there were no casualties after the explosion at the courthouse, but said police were investigtating the blast.

He said: “There was an explosion behind the court, we are investigating.”

He said: “It is not a blast. A special taskforce group detected a bomb on the suspicious motorbike.

“They tried to open the seat but because it had been stuck they decided to carry out a controlled blast.”

The fears have erupted after eight bombs exploded in churches and hotels on Sunday, with the current death toll standing at 359.

Meanwhile, Sri Lankan authorities have brought in more people for questioning as the probe into the terror attacks, which ISIS have claimed responsibility for.

Police said an Egyptian and several Pakistanis were among those detained overnight.

It has emerged that a group of nine well-educated homegrown Islamist suicide bombers, including a woman, were behind the attacks, with one man believed to have studied in the UK between 2006 and 2007.

Sri Lankan authorites are also looking into ISIS links to domestic terror groups the National Thawheed Jama’ut and Jammiyathul Millathu Ibrahim, who they believed carried out the attack.

The Government has admitted to a “major intelligence lapse” after it emerged they had received warnings about the possibility of attacks, which were not acted on.

Deputy Defence Minister Ruwan Wijewardene said: “We have to take responsibility because unfortunately if the sharing of the intelligence information had been given to the right people, I think that at least this could have been avoided or even minimised.”